Dmax measurements of several papers.

[jp80874]

Thank you Donald and Alex

John Powers

 

[JBrunner]

I though Dmax had to do with only blacks. This doesn't tell us anything about how the final print looks, other then the depth of these blacks. So to try and compare the LOOK of a paper by this measurement is not useful. There are goods reason to know the Dmax, just not comparing the final print.

That is what I was trying to say earlier, but you have said it better.

Could someone who knows comment on the relative differences of these blacks? I don't have a densinometer, so I'm curious, are we splitting hairs here, or are some significant visual appearances being discussed?

Of course "significant" in this case is subjective, but I'm sure someone could comment.

 

[JBrunner]

Reviewing the thread, I see Alex already asked my question, and Donald answered. Thanks guys.

 

[Sandman]

Kentmere Bromide and AZO curves

Here is a comparison between the Kentmere Bromide and new AZO grade 2, both developed in Neutol WA. There seems to be a large difference in how both papers respond to exposure. Neither paper has had selenium toning at this point of testing.

 

[Photo Engineer]

Here is a comparison between the Kentmere Bromide and new AZO grade 2, both developed in Neutol WA. There seems to be a large difference in how both papers respond to exposure. Neither paper has had selenium toning at this point of testing.

Fascinating.

Now, here is an interesting experiment for you.

Read them both again but using transmission densitometry. Please post the results, and I will be glad to explain anything 'unusual' that you see in this new plot.

Oh. I would also suggest that you redo the original pair but with a 50 second, 5 second and 0.5 second exposure using a neutral density set to 'normalize' the positions on the charts as much as possible. You may see something 'unusual' in this as well.

PE

 

[Stephen Benskin]

What one considers black is a relative concept. That's why the useful Dmax in the ISO paper standard is 90% of Dmax. With glossy papers, that falls around 2.0 and with matte papers, around 1.60. If you put these papers side by side, you will see a large difference, but on it's own it will look okay. This is a form of Lateral Adaptation of vision. More specifically, it's part of simultaneous contrast. This is a hugh field, receiving little attention with photographers. And in my opinion, it helps answer many of the perennial questions in photography. Photo Engineers example of the left/right is another example of lateral adaptation.

Since glossy can have a DR of around 2.2, and the average scene has a luminance range of 2.2, you get an approximate 1:1 tonal relationship between the subject and print. Matte doesn’t so tonal differences aren’t a subtle.

It's interesting to note that Lyod Jones found a few exceptions to the DR / LER criteria, “for the soft papers, the density scales of the negative (DR) should in most cases exceed the sensitometric exposure scale of the paper (LER), whereas, for the hard papers, the density scales of the negatives should in most cases be less than the sensitometric exposure scale of the paper (LER).”

Jones concluded, “because of the influence of the brightness distribution and subject matter in the scenes photographed, an accurate prediction cannot always be made of the exposure scale (LER) of the paper which will give a first-choice print from a negative of known density scale (DR)… But what other course is there to follow? Either we must make the best of a somewhat imperfect relationship or face the prospect of having no criterion whatever for choosing the paper contrast grade.”

Some of the perceptual tools that have lead to our survival as a species has cause many headaches over the years for those attempting to define it and its relationship to such things are photography and color.

Sandman, without knowing more about your testing parameters, I’m going to suggest that paper reciprocity is at work in some respect here.

 

[Photo Engineer]

Steven, one of my suggestions in my last post involves a test for reciprocity effect.

I believe that there is a contrast reciprocity effect active in this, and also a coating problem. That is the purpose of the first test I suggest.

Paper, or reflection materials in general involve some peculiar effects when viewed by the human eye. Few people know how or care to test extensively to understand reflection materials. Well then, few people test films completely. They rely on the human eyeball and judgment which are not very good.

I would have suggested the use of goniophotometry in addition, but few people in the world even know what it is let alone have the equipment to measure for it. (It is the essentially the measurement of refllection density as a function of viewing angle and angle of the illuminating light)

PE

 

[sanking]

Ron,

I must say you have intrigued me with the suggestion that the thumbnail curves of AZO No. 2 and Kentmere Bromide 2 show signs of reciprocity effect and a coating problem. To me they just look like normal curves one would expect form these papers, with the caveat that the ES of the new AZO 2 paper is quite a bit shorter than what most people have reported. My own curves of this paper, for example, with both Amidol and Ansco 130, show an ES of around 1.60.

So what is it in the thumbnail curves that suggests reciprocity and a coating problem?

Sandy

Steven, one of my suggestions in my last post involves a test for reciprocity effect.

I believe that there is a contrast reciprocity effect active in this, and also a coating problem. That is the purpose of the first test I suggest.

Paper, or reflection materials in general involve some peculiar effects when viewed by the human eye. Few people know how or care to test extensively to understand reflection materials. Well then, few people test films completely. They rely on the human eyeball and judgment which are not very good.

I would have suggested the use of goniophotometry in addition, but few people in the world even know what it is let alone have the equipment to measure for it. (It is the essentially the measurement of refllection density as a function of viewing angle and angle of the illuminating light)

PE

 

[Photo Engineer]

Sandy, it was actually the problem that people have been having with the last batch of AZO paper that clued me in, as well as some other information such as the fact that AZO really looks best with ultra long exposures which allow lots of dodging.

Bingo! A clue. Something began churning in my mind and suddenly it came to me. Silver laydown error and/or LIRF/HIRF problems.

Oh, that and the fact that I had the same problem making my own AZO here in my DR, which I had to solve. LoL. Yep, BTDT. And, not on purpose.

So, that is my thinking FWIW.

PE

 

[Donald Miller]

Steven, one of my suggestions in my last post involves a test for reciprocity effect.

I believe that there is a contrast reciprocity effect active in this, and also a coating problem. That is the purpose of the first test I suggest.

Paper, or reflection materials in general involve some peculiar effects when viewed by the human eye. Few people know how or care to test extensively to understand reflection materials. Well then, few people test films completely. They rely on the human eyeball and judgment which are not very good.

I would have suggested the use of goniophotometry in addition, but few people in the world even know what it is let alone have the equipment to measure for it. (It is the essentially the measurement of refllection density as a function of viewing angle and angle of the illuminating light)

PE

Am I understanding you to say that reciprocity will account for an increase in contrast on paper just as it does in film?

 

[Stephen Benskin]

Steven, one of my suggestions in my last post involves a test for reciprocity effect.

I believe that there is a contrast reciprocity effect active in this, and also a coating problem. That is the purpose of the first test I suggest.

Paper, or reflection materials in general involve some peculiar effects when viewed by the human eye. Few people know how or care to test extensively to understand reflection materials. Well then, few people test films completely. They rely on the human eyeball and judgment which are not very good.

I would have suggested the use of goniophotometry in addition, but few people in the world even know what it is let alone have the equipment to measure for it. (It is the essentially the measurement of refllection density as a function of viewing angle and angle of the illuminating light)

PE

PE,

Sorry, I must have missed it.

Most text book like photo books usually have a chapter on perception. I'm suggesting an awareness. Not only is it kind of cool to know, but I think you can benefit from knowing the brain will tend to increase the contrast of a scene, so it can look good to a photographer but not look good on film. Knowing that there isn't a strict relationship between negative density range and paper log exposure range is comforting. I know that no system is perfect and shouldn't be obsessively adhered to. To know that the interrelationship of tones on the print play as large or a larger part than just a densitometric number can only benefit. You don't need to be a scientist or have expensive equipment for that. Knowing a little bit about Photometry is good since Photometry deals with psychophysical aspects, but again the point is not so much about measurement but understanding. BTW, this conclusion shouldn't suggest a sloppy approach either.

Donald,
There's reciprocity in paper just as in film. It's just not as big a thing with paper because exposures are usually longer to begin with and paper exposure times usually aren't calculated using a meter (no need for factoring in reciprocity). AZO is such a slow paper that the effects of reciprocity might be noticable. Personally, I didn't look too closely at the thumbnails, and don't know what kind of testing was done. The test is between two different papers too. So, it isn't a good test to prove reciprocity anyway.

Steve

 

[Photo Engineer]

Am I understanding you to say that reciprocity will account for an increase in contrast on paper just as it does in film?

Donald, many paper exposures cover a larger range of times than film exposures and both contrast and speed can vary over that range. So, the answer is yes, and even more so with paper.

Papers have been made since early times with contrast reciprocity failure built into them, and enlarging papers when compared to contact papers and photofinishing papers have been designed for as many as 3 different exposure ranges.

Just as an example, Ektacolor Professional paper was designed to give the same curve shape with a 10" exposure, that the photofinishing paper was for 0.5". This was due to a severe contrast reciprocity failure over that range by the emulsions. Now, the newer emulsions use addenda to damp that out, but if it were missing or off in the last batch of AZO. Well.......

I leave it to you or someone to test, but the implications of what people out there are seeing suggest that the last batch of AZO made it through Kodaks release test, but now fails to perform. There must be a reason. I suggested two tests for the most probable errors in that batch.

PE

 

[Sandman]

Paper reciprocity might be at play here, but anyone who works with AZO knows how slow this paper is and how such very long exposure times relative to 'normal' paper (eg Kentmere Bromide) are usually required. It makes me wonder if some this paper's admired printing characteristics can be said to revolve around this 'reciprocity result' if it is actually there.

The Kentmere wedge was contact printed with a 7.5 watt bulb at about 30 inches height above the printer. I think the exposure time was about 15 seconds. To print the AZO with fully exposed steps I had to switch to a 75 watt bulb at the same height and increase time to 25 seconds (if memory serves me right, as my notes are not here).

It would be interesting to re-test AZO with increased light for shorter times and see if the shoulders change. If they do, reciprocity is certainly a factor. If I could prove to myself that reciprocity is present in the curve I've posted it would be interesting in an academic sense, but I doubt it would impress a died-in-the-wool AZO user who would probably just say, "So what?" That is, the curve is there and if AZO prints a certain way because of it's shape why not take advantage of it?

I've not given much thought to shortening my printing times with AZO as my usual times (25 to 45 seconds with most negatives) seem to be pretty much in tune with what other AZO printers seem to be doing routinely.

At this time, I've only tested a few papers. I remember how strikingly different the AZO plot first looked when I first saw it. One of the problems, I realize, when posting test results is that a guy like me tests papers and film for my own use and my results might have a limited value for intrepretation by others.

 

[Ryuji]

Paper reciprocity might be at play here, but anyone who works with AZO knows how slow this paper is and how such very long exposure times relative to 'normal' paper (eg Kentmere Bromide) are usually required. It makes me wonder if some this paper's admired printing characteristics can be said to revolve around this 'reciprocity result' if it is actually there.

Probably not so much of the reciprocity law failure. The "flavor" of printing emulsion comes from the toe shape and shoulder shape, as well as where in the curve the transition takes place. If you want to make "old timey" look, you want to make an emulsion with modestly long toe and a gentle shoulder. Usually, modern emulsion manufacturers want to trim the toe to very short make crisp highlights and make better overall tonal rendition in combination with a common film like Tri-X. When T-MAX and Delta came out and people complained about the highlights, one thing they did was to throw in a bit of toe to multigrade papers.

The Kentmere wedge was contact printed with a 7.5 watt bulb at about 30 inches height above the printer. I think the exposure time was about 15 seconds. To print the AZO with fully exposed steps I had to switch to a 75 watt bulb at the same height and increase time to 25 seconds (if memory serves me right, as my notes are not here).

I think those exposure conditions are well within the reciprocity of the two emulsions and I don't think LIRF and HIRF are in effect to any significant effect.

Chloride emulsions are very easily influenced by small amount of impurities (called dopants when added deliberately) so it's hard to say, but except for color papers made in past 10 years, chloride emulsions usually have terrible high intensity reciprocity failure. With HIRF, the curve will have rounder shoulder when the intensity is increased and time is reduced. (Or the entire curve may shift to the right.) That is, with HIRF, the shadow will be less crisp, and sometimes the quality of black is affected. But you probably won't get much visible HIRF with Azo in normal contact printing time. You'd want to use something like 1/10 sec, or use a flash to expose the paper, to get a clearly visible effect of HIRF on curve with a chloride paper. (However, it's very easy to make a lousy chloride emulsion that shows HIRF at 1 to 10 second exposure.)

At this time, I've only tested a few papers. I remember how strikingly different the AZO plot first looked when I first saw it.

There are many ways to throw in a shoulder like that. Modern emulsion engineers would achieve the target curve by blending 3 to 5 emulsions, each of which is nearly optimally sensitized, to get good speed and density with minimal amount of silver used. But Azo is very slow and optimal sensitization is probably not a requirement. And Azo is an old formula and it's possible that the production wasn't transferred to a more modern protocol. In this situation, I've seen that chloride emulsions having more pronounced shoulder when sulfur sensitization is carried out only very modestly, or not at all. Interestingly, suboptimal sulfur sensitization tends to reduce HIRF.

Incidentally, HIRF in chloride emulsions can be very effectively reduced or practically eliminated by (1) gold sensitization, (2) doping with one or more of iridium salts, iron-complex, and ruthenium complex, or both. Gold sensitization is probably out of question for Azo. Gold increases speed, and that's unwanted.

Chloride emulsion with very good HIRF property is currently manufactured for color printing in a system where the paper is exposed by scanning laser beam. In order to expedite the printing time, exposure time of each pixel is on the order of microseconds. This was very challanging for chloride emulsions. (For rapid access processing, chloride emulsions are preferred because of very fast processing time and low rate of replenishment.)

 

[Stephen Benskin]

Papers have been made since early times with contrast reciprocity failure built into them, and enlarging papers when compared to contact papers and photofinishing papers have been designed for as many as 3 different exposure ranges.
PE

I just spent an hour writing a reply and lost it in the upload. So, this will be an abridged version. Anyway, I just want to make a clarification here and it may only be a question of word choice, but reciprocity is a chemical function of latent image formation as described by the Gurney-Mott hypothesis. I believe the theory has been updated, but I don't want to look it up.

Low energy reciprocity failure is a function of latent image stability. Please forgive any incorrect use of terms. I'm a non-chemistry person. The basic concept is that it takes a given number of electrons to create a stable silver atom. When the film is exposed, electrons are trapped in a sensitivity speck site within the silver halide atoms. If enough electrons are trapped, the silver halide atoms reduces to a silver atom. The problem is the shadows have low energy and the silver halide sensitivity specks will tend to lose electrons over time either returning the silver atom back into a non developable silver halide atom or never reaching a stable silver atom to begin with. Camera exposure is increased to increase the potential for a stable silver atom to form. The brighter sections in the exposure don't have a problem with reciprocity and those areas will further increase in density with a corresponding increase in exposure. That's why there is a contrast increase with reciprocity failure.

The stability of the latent image after exposure works in a similar way. Directly after exposure, many site traps will give off electrons causing film speed to fall. Most speed is lost in the first few seconds. It plateaus after a few hours. That's why the ISO speed standard stipulates a hold time between exposure and development.

Age fog is part of latent image stability. Traps will randomly collect free electrons within the silver halide lattice and over time produces developable silver atoms.

 

[Ryuji]

Stephen Benskin's comment about LIRF is largely correct. However, what affects shoulder is HIRF, which reduces contrast, and this is also the weakness of old chloride emulsions. The mechanism for HIRF is that, when a grain is exposed with brief, intense light, too many undevelopable latent subimages are formed but the grain may very well be undevelopable if there is no developable latent image. Gold sensitization reduces HIRF because of decreased developability threshold. Heavy sulfur sensitization worsens HIRF because it would create more sites where latent subimages could be formed. Doping with iridium, ruthenium, iron, etc. reduces or eliminates HIRF because these doping sites trap photoelectrons and release the photoelectrons in a longer time scale, as if the grain received a longer exposure to begin with.

In modern emulsion design, crystals are designed to have a light collecting part and a latent image forming part. The grains are designed to increase surface area (such as tabular grain) to improve the light collecting power. Each grain has LI forming sites, at one or two corners of each crystal. That is, when photoelectrons are generated by exposure, the electrons are separated from photoholes and they are gathered into the LI forming site. This "concentrates" the photoelectron to form latent image very effectively. It's a very nice concept that is very helpful in increasing emulsion speed as well as reducing reciprocity failure. However, tabular crystals are less common in paper because they need longer time to fix, although tabular grain b&w paper emulsion is very suitable for warmtone paper.

 

[Ryuji]

By the way, I have sensitometric curves for all contrast grades of Apex and Velor Black from late 1930s, if anyone is seriously interested in comparing to Azo and modern enlarging papers. One of my bromide printing emulsions is very similar to Velor Black but made by more modern process.

 

[sanking]

It would be interesting to re-test AZO with increased light for shorter times and see if the shoulders change. If they do, reciprocity is certainly a factor. If I could prove to myself that reciprocity is present in the curve I've posted it would be interesting in an academic sense, but I doubt it would impress a died-in-the-wool AZO user who would probably just say, "So what?" That is, the curve is there and if AZO prints a certain way because of it's shape why not take advantage of it?

My point would remain, there is really nothing particular about the AZO 2 curve in your thumbnail, but for the fact that you show a shorter exposure scale (1.37) than most of us who have tested the paper obtained (1.55 or more). However, the basic shape of the toe and shoulder is pretty much vintage AZO. I have plotted curves of AZO 2 from 1926, 1946 and the contemporary period and there appears to be very little difference in the shape of the curve, though the older material had a bit more contrast and slightly higher B+F (1946) and much higher B+F (1926).

Sandy

 

[Photo Engineer]

Low energy reciprocity failure is a function of latent image stability. Please forgive any incorrect use of terms. I'm a non-chemistry person. The basic concept is that it takes a given number of electrons to create a stable silver atom. When the film is exposed, electrons are trapped in a sensitivity speck site within the silver halide atoms. If enough electrons are trapped, the silver halide atoms reduces to a silver atom. The problem is the shadows have low energy and the silver halide sensitivity specks will tend to lose electrons over time either returning the silver atom back into a non developable silver halide atom or never reaching a stable silver atom to begin with. Camera exposure is increased to increase the potential for a stable silver atom to form. The brighter sections in the exposure don't have a problem with reciprocity and those areas will further increase in density with a corresponding increase in exposure. That's why there is a contrast increase with reciprocity failure.

The stability of the latent image after exposure works in a similar way. Directly after exposure, many site traps will give off electrons causing film speed to fall. Most speed is lost in the first few seconds. It plateaus after a few hours. That's why the ISO speed standard stipulates a hold time between exposure and development.

Age fog is part of latent image stability. Traps will randomly collect free electrons within the silver halide lattice and over time produces developable silver atoms.

Steven, what you describe are 3 different things here.

1. Reciprocity failure. This is both HIRF and LIRF and as described here affect both speed and contrast. This is controlled the use of addenda or methodology during the manufacturing process.

2. Latent Image Keeping. This is termed LIK and it is the change in image as a function of keeping after exposure. LIK and both HIRF and LIRF are related and again LIK is controlled by the use of addenda or methodology in manufacturing.

3. Raw Stock Keeping or RSK. This is controlled by another set of addenda or methodologies again during manufacture.

With luck, and since some of these are linked together, they can be controlled by similar or the same treatments, but in other cases, a chemical that makes LIRF better will make HIRF worse and that is not good. It is usually a set of compromises to get the best results for the product intended. I used the example of the professional vs photofinishing grades of color paper above, which used different addenda and treatments, but the same emulsions. In today's color papers, the same emulsions and addenda are used across the board because these probelms have essentially been resolved in the newer emulsions.

I do believe that reciprocity failure is contributing somewhat to the nature of several observations being made about Azo paper. I cannot be certain though, but from all of the posts I have read here and elesewhere, it looks very much as if that is what is going on.

PE

 

[Stephen Benskin]

PE,

Thank you for telling me what I just said.

Steve

 

[Ryuji]

I have plotted curves of AZO 2 from 1926, 1946 and the contemporary period and there appears to be very little difference in the shape of the curve, though the older material had a bit more contrast and slightly higher B+F (1946) and much higher B+F (1926).

Are those curves obtained by your own sensitometry work in recent years or are they obtained from Kodak or third party tests shortly after the emulsions were manufactured?

If you did the sensitometry work, can you comment on the possible difference on the image hue? (especially if you could mention in the case of Dektol 1+4 or something standard without organic antifoggants or amidol)

Also, are those different vintages similar in speed?

Thanks!

Ryuji

 

[sanking]

The tests were done by me within the past couple of years with vintage samples. I still have some of the vintage material and might run farther tests at some point in the future.

Here are my observatons from the plots, based on development in Ansco 130.

First, for AZO 2, comparing the new sample with a 1946 sample.

1. Dmax was approximately the same for the old and new samples.

2. The new AZO was faster by about 2/3 of a stop.

3. The new AZO has a longer exposure scale than the 1946 AZO, log 1.58 versus log 1.42.

4. No apparent difference in hue, but the new AZO appears to have some kind of optical brightened added as it appears visually brighter even though there is not much density in paper white.

AZO 3, new sample versus 1946 sample.

1. Dmax is about log 0.15 higther with the new AZO.

2. The new AZO was faster by about 1/3 of a stop.

3. The new AZO has a slightly shorter exposure scale than the 1946 AZO, log 1.07 versus log 1.16.

4. No apparent difference in hue, but ss with the new AZO 2, the new AZO 3 appears is visually brighter.


Sandy

Are those curves obtained by your own sensitometry work in recent years or are they obtained from Kodak or third party tests shortly after the emulsions were manufactured?

If you did the sensitometry work, can you comment on the possible difference on the image hue? (especially if you could mention in the case of Dektol 1+4 or something standard without organic antifoggants or amidol)

Also, are those different vintages similar in speed?

Thanks!

Ryuji

 

[Ryuji]

Very interesting Sandy. What about 1926 one? Perhaps slightly warmer in tone?

I'm very interested in comparing the image quality of various historical emulsions in line with the development of photographic chemistry and technology.

 

[sanking]

Ryuji,

The 1926 samples have a lot of fog ( in excess of log .20) which makes them difficult to evaluate, both in terms of the hue and the curve. When I have a little time I will run some tests with with BZT added to the developer to lower the B+F. I have been storing the samples since I got them in the freezer to hopefully they will not develop any additional fog in the interval.

Sandy

Very interesting Sandy. What about 1926 one? Perhaps slightly warmer in tone?

I'm very interested in comparing the image quality of various historical emulsions in line with the development of photographic chemistry and technology.

 

[Ryuji]

This is very interesting. Your observation is well in line with the introduction of a very potent and effective antifoggant, 1-phenyl-5-mercaptotetrazole (PMT) for chloride emulsions in late 20s or early 30s. PMT would cool the image hue very much, whether added to the emulsion or developer, so that's why I was curious about the image hue in 1926 version. With that much fog, image fog wouldn't be the same as when the emulsion was fresh, no matter how much BTA or PMT is added to the developer.

Fogging and poor keeping properties of chloride and chlorobromide paper appear to be a VERY common problem; almost all manufacturers had difficulty in early years. Companies like AGFA were well ahead in this game by 1920s, but Fuji was having serious problems in 1930s (they actually hired a German engineer for one year and learned then latest technology from him to overcome this and many many other problems they had). Most companies had better luck with bromide papers, but effective antifoggant and stabilizing agents for bromide emulsions came a bit later.